1. Field of the Invention
The present invention generally relates to a bipolar secondary battery. More specifically, the present invention relates to a bipolar secondary battery that suppresses or interrupts a localized concentration of current in a terminal plate of a bipolar secondary battery resulting from an internal short circuit in the bipolar secondary battery.
2. Background Information
In recent years, there is an urgent need to reduce the amount of carbon dioxide emitted to the atmosphere in order to protect the environment. As the automotive industry looks increasingly to electric vehicles and hybrid electric vehicles as a means of reducing carbon dioxide emissions, bipolar secondary batteries are attracting attention as an electric power source for the electric motors that propel such vehicles. The electric power source is the key to making electric and hybrid electric vehicles practical.
When a bipolar secondary battery is overcharged or incurs a mechanical shock (impact) from the outside, a short circuit typically occurs inside the bipolar secondary battery. Since the energy density of the bipolar secondary batteries currently used is large, an internal short circuit occurring inside the bipolar secondary battery causes localized heating at the portion where the internal short circuit occurred. Since a bipolar secondary battery includes a positive electrode active material layer, a collector, a negative electrode active material layer, and a dielectric layer laminated closely together, localized heating can not readily cool and heat tends to linger in portions where internal short circuits occur.
In order to alleviate the problem of increased temperatures caused by short circuiting in lithium-ion secondary batteries, there is a technology that uses an extremely thin film of aluminum on a positive electrode collector. With that technology, when a short circuit current flows in the positive electrode collector, the thin film of aluminum heats due to the current and disperses the heat, thereby restoring the insulation of the portion where the short circuit occurred and preventing the temperature of the battery from increasing (See, Japanese Laid-Open Patent Publication No. 2003-243038).
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bipolar secondary battery. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.